For vCloud air plugin version 1.5.1.0 this is expected if the vCloud air certificate has not been added to vCenter server trusted keystore. If you don’t add the certificate you will be unable to register your vCloud Air account with the plug-in and connect to vCloud Air.

Solution:

Login to vCloud air. https://vchs.vmware.com

From browser download the certificate.
NOTE Ensure that you select the Base-64 encoded x.509 option while exporting the certificate.
Firefox
– Click the lock icon in the URL field, then click More information.
– In the Security tab, click View Certificate.
– In the Details tab, click Export.
– Save the file with the name vchs.cer and the type X.509 Certificate (PEM).
Internet Explorer
– Click the lock icon in the URL field, then click View certificates.
– In the Details tab, click Copy to File and follow the wizard to export the certificate.
– Select Base-64 encoded X.509 (.CER) as the format and name the file vchs.cer.
Chrome
– Click the lock icon in the URL field.
– In the Connection tab, click Certificate information.
– In the Details tab, click Copy to File and follow the wizard to export the certificate.
– Select the Base-64